1. Field of the Invention
The present invention relates to a method and apparatus for a solid-state laser, and more particularly, of providing a high duty factor (i.e., pulse length×repetition rate), high energy, diode-pumped solid-state laser apparatus and method thereof.
2. State of Technology
Several techniques have been utilized to mitigate the effects of thermal gradients during solid-state laser operation. First, diode pumping to match absorption lines of dopant ions in the gain materials of laser materials, reduces the amount of waste heat generated. Second, convective gas flow across the surfaces of the active medium can help remove heat. Background for such a method is described by Sutton et al., in “Heat Removal in a Gas Cooled Solid-State Laser Disk Amplifier,” AIAA Journal, Vol. 30, No. 2, pp. 431-435, (1992).
Another technique is to allow an active medium, i.e., a laser gain medium, to temporarily store the deposited heat. During laser operation, the active medium will heat up until it reaches some maximum acceptable temperature. The cooling cycle is then begun, in the absence of lasing, and elapsed time between periods of laser operation depends largely on the efficiency of the cooling of the laser during the suspended lasing action. Background for this concept, i.e., the Heat Capacity Laser (HCL), is described in U.S. Pat. No. 5,526,372, issued Jun. 11, 1996 to Albrecht et. al., and assigned to the assignee of the instant application. Additional background for this concept is described in “Solid state heat capacity disk laser,” by Albrecht et al., Laser and Particle Beams Vol. 16, pp. 605-625, 1998.
Another technique is to move a volume of the active medium by translation and/or rotation, in front of a pumping source. The source illuminates only a part of the active medium volume, while the entire volume is being cooled continuously. Background information on such a technique is disclosed in U.S. Pat. No. 4,833,682, titled “Moving Slab Laser,” issued May 23, 1989 to Byer et al.
The emergence of high average power diode arrays beyond the conventional technologies in which typically only a single laser diode bar is attached to a single high performance heat sink have enabled monolithic laser diode packages in which multiple diode bars are attached to a single high performance heat sink. This technology advance has led to larger laser diode arrays and larger diode-pumped laser systems. Background for one such type of package, which utilizes Silicon Monolithic Microchannels (i.e., SiMM) is described and claimed in U.S. Pat. No. 5,548,605 issued Aug. 20, 1996 to Benett et al., U.S. Pat. No. 5,828,683 issued Oct. 27, 1998 to Freitas, and U.S. Pat. No. 5,923,481 issued Jul. 13, 1999 to Skidmore et al., and assigned to the assignee of the instant application.
The instantaneous power provided by these diode arrays needs to be sized for efficient HCL operation, but this power is utilized only a fraction of the time that results in a low duty factor, i.e., the ratio of the time on to the sum of the time on and off times (or, equivalently, pulse length×repetition rate). Since diode cost is about proportional to instantaneous power, (i.e., the optical power output for the time period on), and not average power, (i.e., the product of the instantaneous power and the duty factor), the low duty factor results in a cost penalty inversely proportional to the duty factor. This cost penalty is large since diode array cost dominates laser system cost.
Accordingly, the present invention provides a solution for increasing the duty factor for solid-state lasers pumped by exemplary diode arrays.